﻿using System;
public class thanhluan
{
    public static int Main()
    {
   
        double bankinh;
        double dientich;
        Console.Write("nhap ban kinh:");
        bankinh = double.Parse(Console.ReadLine());
        dientich = bankinh * bankinh*Math.PI;
        Console.WriteLine("dientich:{0}", dientich);
        //Console.WriteLine();
        return 0;
    }
}